The present invention relates to a compressor torque estimate device for estimating a torque required for driving a variable displacement compressor and an engine control device.
For example, as a refrigerant compressor in an air conditioner for a vehicle, there is a variable displacement compressor whose displacement can be changed based on a compressor control signal from an external device. When the displacement of the variable displacement compressor is changed, a torque (a compressor torque) required for driving the compressor is also varied.
Therefore, conventionally, in order to appropriately operate an engine of a vehicle as a drive source of the variable displacement compressor, the compressor torque is estimated, and an output torque of the engine is controlled by considering the compressor torque (e.g. page 8 and FIG. 6 in Japanese Patent Unexamined Publication No. 2001-180261). Although there is a method in which the compressor torque is directly detected with a torque sensor, the torque sensor is relatively expensive and increases cost. Accordingly, in a technique disclosed in Japanese Patent Unexamined Publication No. 2001-180261, the compressor torque of the variable displacement compressor is estimated based on the compressor control signal.
In the above method for estimating the compressor torque based on the compressor control signal, when the variable displacement compressor is during a steady state, the compressor torque can be estimated with a relatively high accuracy, that is, a difference between an estimated compressor torque and an actual torque (an actual compressor torque) is relatively small. However, in a time of transition when the displacement of the variable displacement compressor is rapidly excessively changed, for example, when an air conditioner switch is turned on or off, when the rotational speed of the engine is suddenly changed, when a set temperature is changed, or when an amount of air blowing out from the air conditioner is changed, the difference between the estimated compressor torque and the actual torque becomes large due to delay (mechanical response delay) of mechanical movement in a displacement-varying operation.
For example, when the air conditioner switch is turned on from an OFF-state, a compressor control signal for changing to a maximum displacement is supplied from an external device to the variable displacement compressor, which is in a minimum displacement state. Therefore, the compressor torque is estimated based on the compressor control signal as an instruction for changing to the maximum displacement when the air conditioner switch is turned on.
However, the displacement of the variable displacement compressor becomes the maximum late from the instruction for changing to the maximum displacement due to the mechanical response delay as mentioned above. Therefore, as shown in a graph in FIG. 4, an extremely high torque value as the compressor torque (a solid line) is estimated almost as soon as the air conditioner switch is turned on. On the other hand, an actual torque (a dotted line) gradually increases from a low torque value. Therefore, during a certain period from a time when the air conditioner is turned on, the difference between the estimated compressor torque and the actual torque becomes large. During the certain period when the difference is large, an output torque of the engine cannot be appropriately controlled. The engine excessively rotates, and gasoline mileage and drivability of the vehicle deteriorate.